Branched-chain amino acids refer to three kinds of amino acids (i.e., L-valine, L-leucine, and L-isoleucine) and they are known to be mainly metabolized in the muscle and used as an energy source during physical activity. Along with the increased awareness with respect to the important roles of these branched-chain amino acids in maintaining and increasing muscle mass during physical activity, their use is also on the rise. In particular, L-leucine is an essential amino acid and is widely used in medicines, foods, feed additives, industrial chemicals, etc.
Meanwhile, these branched-chain amino acids are mainly produced by microorganisms of the genus Escherichia or the genus Corynebacterium, and are known to be biosynthesized from 2-ketoisocaproic acid, a precursor, after undergoing several steps from pyruvic acid (Korean Patent Nos. 10-0220018 and 10-0438146). However, the enzymes involved in the leucine biosynthesis have a problem in that they undergo feedback inhibition caused by the final product, i.e., L-leucine or a derivative thereof, thus making it difficult to perform large-scale industrial production of L-leucine.